As radio-frequency (RF) and optical electromagnetic signals do not propagate well under the ocean surface or through land, alternative communication methods are to be used for these environments. There are multiple alternative options, each having advantages and disadvantages. Therefore, different approaches may be taken depending on applications. For example, some applications may use a tether to communicate by wire or optical fiber, which can impose maneuvering limits or hazards involving physical contact with vehicles or structures. As another example, acoustic communications are often used, but are affected by multipath and shallow-water resonances, with the consequence that robust acoustic communications have a very low bit rate. Yet, another candidate can be near-field magnetic communications, which works with low-frequency signals, to be measurable at longer ranges thereby limiting bit rate, and signals which have a rapid drop off in signal strength at longer ranges.
Recent undersea systems research has shown that manipulating the shape of the magnetic field changes over time can provide more information, either for higher bit-rate communications or for difficult-to-counter short-term magnetic pings. This is a departure from traditional magnetic field signal shapes, which are sinusoidal and involve a number of cycles because LC circuit techniques can be used to efficiently vary the magnetic field through a resonance of the LC circuit. Achieving similar energy efficiency in a magnetic field drive circuit and allowing the shape of each cycle of the waveform to be controlled, for example, amplitude modulated, are desired.